So that you don't contaminate the stopper with anything on the table. Also, if you lay it on it's side, there's a possibility that it rolls off the table and breaks.
A pentagon has five flat sides
One flat surface is a table. Many flat surfaces are facets.
Hexagon :)
A cuboid has 6 sides/faces/flat surfaces.
Yes and it can have 3 or more straight sides
So they don't roll.
So that whatever leftover gunk happens to be on the table doesn't get all over the part of the stopper that goes into the bottle, contaminating the contents.
A table shaped hill with a flat top and steep sides is called a plateau.
There are six flat sides
There are 2 completely flat sides on every cylinder.
square
A triangle has three sides !
Faces are sides but sides (as in sides of a square) need not be faces.
A pentagon has five flat sides
It is a pyramid.
A table
Trapezoid.